1. Field of the Invention
The present invention relates to electron image photography for high performance night and all-weather application.
2. Description of the Prior Art
The range of transmission of electromagnetic radiation through the atmosphere varies with the wavelength of the radiation and the weather conditions. Thus, rain and fog can attenuate optical wavelengths drastically, but leave some longer wavelengths relatively unaffected. This is in part due to the reduction in Mie and Rayleigh scattering at the longer wavelengths. The possibility of using millimeter waves for high-performance night and allweather imaging systems has been discussed in the paper, B. Levin and B. Feingold, "All-Weather Eye Opens Up With Millimeter Wave Imaging", Electronics, Aug. 17, 1970, pages 82-87. These authors note that absorption, caused by the resonant behavior of the water vapor and oxygen molecules, accounts for most of the attenuation in the millimeter-wave range. However, a number of low-attenuation windows exist in the millimeter band centered at 35 GHz. (8.6 millimeters), 94 GHz. (3.2 millimeters), 140 GHz. (2.15 millimeters), 240 GHz. (1.25 millimeters), and 28.3 THz. (10.6 microns). There are no perfect windows, but there are best selections. Thus, one of the best windows for clear air, light fog, and light and heavy rain conditions is at 10.6 microns. However, a heavy fog blocks it at 50 decibels per kilometer. The 1.25 millimeter window has 28 decibels per kilometer loss in heavy fog but is not as good as the 10.6 micron window for other weather conditions.
Until recently little has been done with the millimeter wave region. A known prior art millimeter imaging device utilizes a Germanium panel and a raster screen readout system.